The invention relates to a filter device, particularly an air breather filter device for a tank, and an arrangement for ventilating a tank comprising a filter device.
Air breather filters are commonly utilized in vehicles, particularly commercial vehicles such as trucks and buses. They consist of filter paper to be able to catch especially small particles of down to 4 μm and smaller. These small particles are difficult to filtrate on fuel filters. Trapping these small particles increases the lifetime of engine components such as fuel pump and injectors strongly. When the filter paper gets wet, the pressure drop through the filter paper is increased dramatically. An amount of only 5 g diesel is enough to fully soak existing filter papers and changes the pressure drop over the filter from 0 mbar to around 20 to 30 mbar. This pressure drop has a negative impact on engine startability, lowers the maximum torque and increases the fuel consumption on all trucks somewhat.
Leakage of fuel from inside of the tank through the fuel sender can occur in various situations such as hilly driving, sloshing due to braking, curves, accelerations, parking in slopes, etc. This leakage is causing filter papers of air filters connected to the fuel tank to get soaked with fuel, leading to an increased pressure drop. This pressure drop causes an unbalance of fuel levels on dual tanks which are commonly used in commercial vehicles, as each tank has its own air filter, and clogging occurs mainly on master side. For instance, a pressure drop around 20 to 30 mbar on the master tank filter and 1 mbar on the slave tank filter corresponds to 240 to 360 mm of level difference which may correspond to a significant portion of the fuel tank height. The result is that a significant amount of fuel cannot be consumed also the fuel is carried in the tank.
US 2006/0157117 A1 discloses a filter device in a fuel tank venting system which includes a fuel cap, a vent diaphragm and a vent disc. A valve cavity with a substantially concave bottom is formed in a bottom of the fuel cap. An air passage is formed through the vent disc. A convex surface is formed on a top of the diaphragm projection. The vent diaphragm is retained between the concave bottom and the convex surface. When air is needed for fuel flow, a vacuum within the fuel tank pulls the perimeter of the diaphragm downward, which breaks a seal with the concave bottom to allow air flow which enters the system through an air filter arranged above the diaphragm.
It is desirable to provide a filter device which can avoid soaking of the filter paper due to fluid entering the filter device through the outlet of the filter device.
It is also desirable to provide an arrangement for ventilating a tank comprising at least one filter device.
A filter device, particularly an air breather filter device for ventilating a tank, comprising a housing with a first port being provided as an inlet in normal operation of the filter device and a second port being provided as an outlet under normal operation of the filter device, the housing enclosing at least one filter and an air passage extending from the first port to the second port passing through the filter. Inside the housing a baffle unit is arranged in the housing for covering the at least one first filter in relation to the second port, wherein the baffle unit is arranged to deflect a fluid flow entering the filter device through the second port.
Favourably, the normal operation of the air filter is undisturbed in case a leakage of fuel from inside of the fuel tank occurs. The fuel leaking into the filter device can be evacuated from the filter device without contaminating the filter. The baffle unit is advantageously arranged to deflect a fluid flow coming from the second port so as to prevent the fluid flow hitting the filter directly. The baffle may separate the fluid flow leaking into the filter device into a flow of predominantly liquid fluid and a flow of gaseous fluid, wherein the gaseous flow can enter the filter. Expediently, the baffle unit may be arranged to encourage dripping of a liquid from the baffle unit. Hence, in case of diesel as liquid fluid, creeping of the diesel into the filter can be avoided. The liquid fluid is guided to circumvent the filter reliably.
Expediently, the tank can be a fuel tank, particularly a dual fuel tank where a master and a slave tank are coupled. The tank can also be a urea tank, particularly suitable in cases where the filter device has to be installed below the maximum liquid level.
According to an advantageous embodiment, the baffle unit may split a fluid flow entering the filter device through the second port into a first flow of a gaseous fluid passing the filter towards the first port and a second flow of a liquid fluid flowing along an outside of the outer shell to a bottom portion of the housing. The liquid flow can be reliably deterred from entering the filter.
According to an advantageous embodiment, the baffle unit may comprise a deflector plate facing the second port and overlapping an orifice of the second port. A flow deviation of the leakage fluid flow is enforced by the deflector plate. Particularly, the deflector plate may have a convex profile towards the second port. The shape of the deflector plate can be used to enhance the possibility of draining the liquid from the deflector plate in an area away from the filter, for instance by providing an umbrella-like profile.
Particularly, a passage may be provided from the deflector plate to the outside of the baffle unit which guides a liquid fluid from the deflector plate to the outside of the baffle unit towards the bottom part. Advantageously, the passage enforces a flow path for the liquid fluid thus blocking the fluid from entering the first filter.
According to an advantageous embodiment, the baffle unit may have a shell extending between the first and the second port, the shell being terminated at its side intended to be arranged proximate to the second port by a cover arranged at a distance from the deflector plate. Advantageously, the cover may have a maximum height in its middle. Liquid is prevented from dripping into the filter covered by the cover. In case liquid would hit the cover, the curvature of the cover guides the liquid away from the centre of the cover. Expediently, an orifice is provided in the centre of the cover, providing an outlet for fluid passing the filter inside the baffle unit in normal operation. Advantageously, the cover may include an orifice for passing a fluid. For instance, the orifice may be a tube with openings for the fluid, the tube extending from the cover towards the second port. The tube may support the deflector plate, thus increasing the stability of the baffle unit.
According to an advantageous embodiment, the cover and the deflector plate may enclose a portion of the air passage between the first port and the second port. A fluid flow leaking in through the second port has to perform two deflections by about 180° each in order to enter the orifice in the cover.
According to an advantageous embodiment, the baffle unit may have a collar pointing outwardly. Particularly, the collar may be arranged at the bottom of the baffle unit opposing the cover. Particularly, the collar may comprise one or more openings. Fluid flow can pass through the collar.
According to an advantageous embodiment, a second filter may be arranged in a fluid passage between the baffle unit and the first port, the fluid passage being arranged outside the first filter. The fluid passage may be provided for liquid fuel coming from the second port. Expediently, the second filter may be arranged concentric with the at least one filter in the baffle unit. Alternatively, the second filter may be an additional filter element arranged eccentrically to the at least one first filter.
The second filter may be used as fuel filter. The second filter may be made of the same material as the at least one filter enclosed in the baffle unit. The second filter may be made of paper or of fibres, particularly plastic fibres. Favourably, the second filter has filter characteristics equal or at least similar to the first filter. Using plastic fibres, e.g. polyester, makes it easier to secure a sealing between the material of the second filter and the material of the housing, e.g. via a welding process, compared to paper as filter material.
The second filter may be ring-shaped or washer-shaped. The second filter secures filtration of the gaseous fluid, e.g. air, in case it is not soaked by the liquid fuel, e.g. diesel or urea or the like, and guarantees a release of liquid without soaking the at least one filter itself.
According to an advantageous embodiment, the collar may cooperate with, particularly overlap, the second filter. Expediently, the collar can be used to stabilize the second filter.
According to an advantageous embodiment, the baffle unit may comprise means for blocking a liquid film on the baffle unit to creep into the at least one filter. Such means may be one or more of an undercut at an underside of the deflector plate, a groove at the underside, a labyrinth geometry, for instance a suitable edge structure at a flow passage of the liquid fluid, or any combination thereof. Particularly, the filter device may be provided with a labyrinth geometry for sealing between parts in the filter device. For instance, the labyrinth geometry may be arranged between the first port and the second filter, thus protecting the second filter and the first filter from water entering through the first port. Such a situation can happen when the filter device is mounted in a vehicle where the filter device experiences rough conditions during use of the vehicle. For instance, rain water can enter the filter device under unfavourable conditions.
According to an advantageous embodiment, the housing may comprise a conical bottom portion. Advantageously, the conical bottom reduced the speed of the gaseous fluid in the filter device thus being favourable for the pressure drop in the filter.
According to another aspect of the invention, an arrangement for ventilating a tank, wherein a filter device is provided, comprising a housing with a first port being provided as an inlet in normal operation of the filter device and a second port being provided as an outlet under normal operation of the filter device, the housing enclosing at least one filter and an air passage extending from the first port to the second port passing through the filter, and wherein inside the housing a baffle unit is provided covering the at least one first filter in relation to the second port, wherein the baffle unit is arranged to deflect a fluid flow entering the filter device through the second port.
Advantageously, the invention can be used for ventilating of tanks which require gas filters, particularly air filters, where there is a risk that a liquid fluid may enter the filter device through the outlet of the filter device. A favourable usage is made in fuel tank arrangements, such as dual tanks where fuel is transferred from a slave tank to a master tank, or urea tanks where the air filter has to be installed below the maximum urea level in the urea tank.
Particularly, the baffle unit may shield the at least one filter against the second port. Expediently, the filter is protected against liquid fluids entering the filter device through the outlet port.
According to an advantageous embodiment, the at least one filter device is arranged at a master tank of a dual tank system to which fuel is supplied from a second tank of the dual tank system. Advantageously, the risk of an undesired pressure drop on the master tank filter which may correspond to a significant portion of the fuel tank height can be avoided. As a result the amount of fuel available in the slave tank can be consumed in the master tank.